I vote for anything slow at the end of the night that inevitably brings you down. Living in Louisiana it is not like you are going to head to the bar and find you that special someone to take home at the end of the night every time you go to the bar. That only happens on special nights when someone has way to much alcohol and way to little sense. Most nights you are chilling at the bar having a good time with your friends when 12:30 rolls around (most places in the world that is when you start heading to the bar) and they start playing the slow music. It kinda takes everyone out of their happy place and makes them look around and realize how depressing everything is.
Some dude made up a list of 14 Songs You Should Never Play in a Bar that I for the most part agree with. His comments are pretty funny.